The present invention is concerned with an improved wire wrap tool capable of use either manually or in conjunction with an appropriate power drive, and operative to provide one or more wraps of wire about a terminal which is engaged by the tool to form an electrical connection to the terminal.
The basic principles of wire wrap tools have long been known in the art and are discussed, for example, in Mallina U.S. Pat. No. 2,759,166, issued Aug. 14, 1956, for "Wrapped Electrical Connection". Over the years, a wide variety of such tools, ranging from simple hand-held and hand-rotatable tools to computer controlled completely automatic high speed machines, have been developed and used in the industry. The Mallina tool contemplated that the wire being wrapped might have an enamel or insulating coating thereon, and relied on forces between the wire and the terminal being wrapped to crush the insulation at a number of spaced points along the wire to achieve a metal-to-metal contact between the conductor wire itself and the terminal being wrapped. This crushing technique, however, is not reliable to achieve the desired electrical contact in all cases, and the Mallina approach in this particular respect was therefore discarded, in subsequent developments, in favor of alternative approaches wherein the wire being wrapped had no insulation at all thereon, or wherein, if an insulated wire was to be wrapped, a length of the wire was completely stripped of all insulation either in a separate preliminary operation or by an appropriate insulation stripper included in the tool.
Prior patents which disclosed wire wrap tools adapted to wrap either bare wire, or wire which has been prepared by complete removal of a length of insulation therefrom before being supplied to the tool, include Ackerman U.S. Pat. Nos. 3,788,367 and 3,670,784, Baker et al U.S. Pat. No. 3,625,262, Hannify U.S. Pat. No. 3,618,641, Lamoureux U.S. Pat. No. 3,318,344, Olds et al U.S. Pat. No. 3,078,052, Zoltai U.S. Pat. No. 3,250,302, Emberson et al U.S. Pat. No. 3,066,879, Miklau U.S. Pat. No. 2,785,797, and Beaulieu et al U.S. Pat. No. 2,648,356. In general, tools of this type require that the wire to be wrapped first be cut to proper length and stripped for about an inch or so at each end. One stripped end is then threaded into a slot at the end of the tool whereafter the tool and wire is placed over a post or terminal to be wrapped and the tool is rotated, either by the user's fingers or by a small motor, to wrap the wire tightly around the post or terminal. This procedure is comparatively slow and tedious.
In an effort to expedite the operation somewhat by eliminating the need to prestrip the wire before it is threaded into the wrapping tool, tools have been suggested which include means therein for completely stripping a length of insulation from the wire end being wrapped as the wire is being fed from an appropriate supply on or associated with the wrapping tool. Arrangements of this type are disclosed in Skutt et al U.S. Pat. No. 3,803,649, Baker et al U.S. Pat. No. 3,781,932, Staiger U.S. Pat. No. 3,628,402, Finn et al U.S. Pat. No. 3,619,829, deRose et al U.S. Pat. No. 3,554,243, Zoltai U.S. Pat. No. 3,394,742, Finn U.S. Pat. No. 3,393,715, Wood el al U.S. Pat. No. 3,378,048, Belek et al U.S. Pat. No. 2,807,810, and Miloche U.S. Pat. No. 2,682,063. Tools of this latter type are, in general, somewhat more complex than those intended to wrap bare or prestripped wire. Moreover all such tools have the major disadvantage that the wire wraps are completely devoid of insulation.
In this latter respect, even with the low voltages (3.6 volts for RTL logic to 18 volts for CMOS) used in modern electronics applications, it is far more advantageous to provide wrap connections which have insulation thereon, so that the outer periphery of the wrapped wires remains insulated to reduce the possibility of short circuits to densely packed neighboring posts and wires. The complete stripping of the insulation from the wire being wrapped, either before it is fed through the wrapping tool or at the time it is being so fed, makes it impossible to achieve this important advantage.
In contrast, and as will be discussed more fully hereinafter, the present invention provides a tool which supplies insulated wire from a spool directly to wrap-posts without the need for prestripping and/or precutting the wire. The tool does not remove insulation from the wire in the usual sense, but merely slots the insulation to expose a portion of the underlying conductive wire while leaving the remaining insulation intact. A 20 to 35% reduction in the number of connections required can be achieved, and all points which are to be electrically interconnected in a circuit can be serviced with one continuous strand of wire in "daisy chain" fashion. More than one level is rarely required, with the result that the wrap posts can be significantly shorter (about half the usual length) and with the further result that less space between stacked wiring cards is needed, i.e., there can be a 40 to 60% decrease in inter-board spacing. Since the wrap connection on each post or terminal is fully insulated from adjacent terminals, terminals can be placed closer together without danger of accidental shorting, thereby accomplishing a further degree of compactness in design while simultaneously achieving increased reliability. Moreover, in a normal wire wrap assembly the wires are often pulled tight at the corners against the sharp edges of the extending terminals with the result that vibration and heat may cause short circuits to occur; but with a single-connection height terminal wrapped with insulated wire, as is achieved by the present invention, this potential problem is also avoided.